WO2012109284A2 - Matériaux hybrides durcis dans la glace - Google Patents

Matériaux hybrides durcis dans la glace Download PDF

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WO2012109284A2
WO2012109284A2 PCT/US2012/024200 US2012024200W WO2012109284A2 WO 2012109284 A2 WO2012109284 A2 WO 2012109284A2 US 2012024200 W US2012024200 W US 2012024200W WO 2012109284 A2 WO2012109284 A2 WO 2012109284A2
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composite
polymer
particles
ceramic
sample
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WO2012109284A3 (fr
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Ulrike G.K. WEGST
Philipp M. HUNGER
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Dartmouth College
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L5/00—Compositions of polysaccharides or of their derivatives not provided for in groups C08L1/00 or C08L3/00
    • C08L5/08—Chitin; Chondroitin sulfate; Hyaluronic acid; Derivatives thereof
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
    • A61L27/00—Materials for grafts or prostheses or for coating grafts or prostheses
    • A61L27/40—Composite materials, i.e. containing one material dispersed in a matrix of the same or different material
    • A61L27/44—Composite materials, i.e. containing one material dispersed in a matrix of the same or different material having a macromolecular matrix
    • A61L27/446—Composite materials, i.e. containing one material dispersed in a matrix of the same or different material having a macromolecular matrix with other specific inorganic fillers other than those covered by A61L27/443 or A61L27/46
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L89/00—Compositions of proteins; Compositions of derivatives thereof
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
    • Y10T428/2982—Particulate matter [e.g., sphere, flake, etc.]
    • Y10T428/2991—Coated

Definitions

  • nanoarchitecture can be carefully tailored. Because the introduction of porosity significantly lowers the mechanical properties of a material, it is difficult to achieve a successfull compromise between porosity and mechanical performance. Furthermore, it is a great challenge to modify structure and mechanical performance independently.
  • Nacre is of considerable interest because of its exceptional property profile, such as high stiffness and strength with high toughness.
  • Nacre is a fully dense material with a brick-and-mortar structure composed of 95 vol% ceramic (aragonite) platelets and 5 vol% polymer (protein) glue.
  • a number of published studies describe various processing routes. However, these are limited by the small sample sizes that can be generated— frequently films of only several tens of micrometers in thickness— and highly labor intensive processing techniques, such as the layer-by-layer assembly of micrometer-sized ceramic platelets. Only one method produces larger scale samples, but results in much coarser structural features than those of the natural material. It relies on the infiltration of a porous ceramic scaffold with a polymer prior to crushing, producing fully dense nacre-like materials.
  • This disclosure advances the art and overcomes the problems outlined above by providing devices and methods for freeze casting of metal-polymer composite, ceramic-polymer composite and polymer-ceramic composites.
  • freeze casting and by taking a biomimetic approach it is possible to create composite scaffolds whose mechanical properties and hierarchical architecture can be controlled over several orders of magnitude and at several length scales.
  • a metal-polymer composite scaffold includes metal particles coupled with polymer binder, the scaffold having regions of aligned porosity with a gradient.
  • the metal particles include stainless steel.
  • the metal particles have sizes equal to or smaller than 3 ⁇ .
  • the scaffold has Young's modulus is below 950 MPa.
  • the polymer binder includes chitosan and gelatin.
  • the composite also includes ethanol.
  • the composite has porosity of at least 70%.
  • a ceramic-polymer composite includes alumina and polymer binder, the composite having regions of aligned porosity with a gradient.
  • the composite has a porosity of at least 90%.
  • the polymer binder includes chitosan and gelatin.
  • the alumina is in a form of particles or platelets.
  • the composite formed with the alumina in the form of platelets has less shrinkage and improved yield strength and Young's modulus than a ceramic-polymer composite formed with the alumina in the form of particles.
  • the alumina particles have diameters in the range of a few hundred nms.
  • the alumina particles have diameters in the range of approximately 10 ⁇ .
  • the alumina particles include a first portion of particles with diameters in the range of a few hundred nms and a second portion of particles with diameters in the range of approximately 10 ⁇ .
  • a multi-functional polymer-ceramic composite includes glass beads and polymer binder; the composite having regions of aligned porosity with a gradient.
  • the glass beads are selected from a group consisted of hollow beads, solid beads, and flakes.
  • the polymer binder includes chitosan.
  • the multi-functional polymer-ceramic composite has a reflectivity above 80% in a visible and IR spectra ranging from 250 nm to 2500 nm.
  • the multi-functional polymer-ceramic composite has thermal conductivity below 0.1 W*m "1 K "1 .
  • the glass beads have sizes ranging from 2 ⁇ to 25 ⁇ .
  • FIG. 1 is a schematic diagram of a freeze caster set up in an embodiment.
  • FIG. 2 is a P-T phase diagram of water with a path of freeze casting and freeze drying in an embodiment.
  • FIG. 3 is a schematic flow chart of a freeze casting process in an embodiment.
  • FIG. 4 is an X-ray tomographic reconstructions of a freeze cast ceramic composite sample with a diameter of 0.6mm. Freezing rate: 20C/min (a) and 5C/min (b) in an embodiment.
  • FIG. 5 is a SEM image illustrating anisotropic growth of lamellar ice in an embodiment.
  • FIG. 6 is a simplified diagram illustrating lamellar crystals with their c-axis ( ⁇ 0001>) growing along a-axis ( ⁇ 1120>) in an embodiment.
  • FIG. 7 is a schematic representation of the general microstructure of porosity within a freeze cast sample in an embodiment.
  • FIG. 8 is a plot of plateau strength against Young's modulus for scaffolds including different particles sizes of particles and size distributions, frozen at two different freezing rates of l°C/min and 10°C/min in an embodiment.
  • FIG. 9 illustrates scanning electron micrographs of composite cell walls of hybrid scaffolds made from a) small particles b) bimodal particles c) large particles. Scale bar is 5 ⁇ in an embodiment.
  • FIG. 10 is a representative compression curve for scaffolds made from small particles in an embodiment.
  • FIG. 11 is a representative compression curve for scaffolds made from large particles in an embodiment.
  • FIGs. 12A-C are three SEM images of 316L stainless steel scaffolds from the third sintering trial at 1150°C in an embodiment.
  • FIGs. 13A-B illustrate two SEM images of cross sections
  • FIG. 14 is a SEM image indicating how the pore sizes and wall thicknesses were measured, in an embodiment
  • FIGs. 15A-D are four tomographic reconstructions of samples S10 (a, b) and S10E (c, d). Images a and c show a full3D reconstruction of the samples. The colored planes on the cubes shows a cross section perpendicular to the scaffold's freezing direction. Images b and d show these cross sections in 2D. The cubes and cross sections had 1 mm side lengths in an embodiment.
  • FIG. 16 is a typical compressive stressstrain curve for a 316L stainless steel freeze cast sample in an embodiment.
  • FIG. 17 is a graph showing the yield strength versus Young's modulus of the samples in an embodiment.
  • FIG. 18 is a graph showing relative Young's modulus plotted against relative density in an embodiment.
  • FIG. 19 is a graph showing relative yield strength plotted against relative density in an embodiment.
  • Fig. 20 is a plot of yield strength against Young's modulus for scaffolds including different particles sizes and size distributions, frozen at two different freezing rates of l°C/min and 10°C/min in an embodiment.
  • FIG. 21 are optical images showing the overall core-shell assembly in an embodiment.
  • FIG. 22 are cross-section of freeze-east scaffolds perpendicular to the freezing direction showing the high degree of alignment of the platelets in the composite walls in an embodiment.
  • FIG. 23A is a schematic showing the hypothesized platelet alignment during directional solidification in an embodiment.
  • FIG. 23 B is a focused ion beam cut through an individual lamella showing the high degree of alignment of the platelets and the nacre-like arrangement within the composite walls in an embodiment.
  • FIG. 23 C is a plot of toughness obtained with the different scaffold types plotted against the achieved Young's modulus in an embodiment.
  • FIG. 24 is a typical stress/strain curve of the investigated hybrid scaffolds. Young's modulus was determined from the initial linear region of the curve while the yield strength was taken as the stress at which the material left the linear region and the slope of the curve changed significantly. Toughness was determined as the area under the stress-strain curve up to a strain of 60% in an embodiment.
  • FIG. 25 is an X-ray microtomography data visualized with the Avizo Standard software package. Edge length of the cube is 500 ⁇ in an embodiment.
  • FIG. 26 are UV-Vis-NIR reflectance spectra with various fillers from 250 nm to 2500 nm in an embodiment.
  • FIG. 27A is a SEM image of a broken strut showing encapsulated hollow glass microspheres at 1600X magnification in an embodiment.
  • FIG. 27B is a SEM image of a glass sphere encapsulated in chitosan polymer, image is shown at 15170X magnification in an embodiment.
  • FIG. 28 is a plot of Log Avg. Yield Strength vs. Log Avg. Modulus in an embodiment.
  • FIG. 29 is a SEM image of a polymer scaffold in an embodiment.
  • FIG. 30 illustrates longitudinal view and traverse view of a scaffold in an embodiment.
  • FIG. 31 illustrates stress vs strain curves for nanocellulose reinforced composites in an embodiment.
  • FIG. 32 illustrates yield strength vs modulus curves for nanocellulose reinforced composites in an embodiment.
  • FIG. 33 illustrates yield strength vs modulus curves for nanocellulose reinforced composites in an embodiment.
  • FIG. 34 are SEM images of nanocellulose reinforced composites in an embodiment.
  • FIG. 35 illustrates yield strength vs modulus curves for nanocellulose reinforced composites in an embodiment.
  • FIG. 36 illustrates stress vs strain curves for nanocellulose reinforced composites in an embodiment.
  • FIG. 37 illustrates six thermal couples for measuring temperatures during freeze casting in an embodiment.
  • FIG. 38 illustrates CAS and CAP samples CAP in an embodiment.
  • FIG. 39 shows a sintering cycle for CAS and CAP in an embodiment.
  • Freeze casting is a processing technique that is based on the unidirectional freezing of a liquid carrier, either within a polymer solution or with particles (metal or ceramic) in suspension.
  • the freezing vehicle for freeze casting is water, although other carriers, such as camphene. Camphene is an attractive freezing vehicle because it has a freezing temperature of about 33°C, allowing the camphene slurries to surely be frozen at room temperature. It was found that by using water as opposed to camphene, unidirectional freezing could be carried out with greater control in our laboratory.
  • the set up of the freeze casting device is shown in FIG. 1.
  • Slurry was prepared.
  • the freeze casting process begins with the preparation of an aqueous slurry. Though primarily water, the slurry also consists of a polymer solution, metal particles, or ceramic particles.
  • a binder material is used to provide additional strength to the green body freeze cast sample prior to sintering. Frequently, a dispersant is added to enhance particle dispersion within the slurry.
  • the slurry is thoroughly mixed so that the particles are evenly dispersed throughout. It is usually also degassed directly before freezing and then it is transferred into an insulating polytetrafluoroethylene (PTFE) cylindrical mold with a conductive bottom. For freezing, the mold is placed onto a copper cold finger that is submerged in a bath of liquid nitrogen.
  • PTFE polytetrafluoroethylene
  • a slurry When a slurry is ready to begin the freezing process, it is poured into a PTFE mold. This mold is placed onto a copper rod that is submerged in a liquid nitrogen bath. The cooling rate of the copper cold finger is controlled by a ring heater around the copper rod and a thermocouple below the mold. The sample is frozen from the bottom to the top.
  • the sample is completely frozen, it is removed from the mold in which it was frozen and lyophilized (freeze dried). Initially, in the freeze casting process, the sample is in liquid form. From this state, the sample is directionally frozen. After freezing, the sample is lyophilized. These phase transitions are shown in FIG. 2. During the lyophilzation process, the ice lamellae transition directly from the solid to the gaseous phase as the sample is put under low pressure vacuum while frozen. Once the ice is removed and the sample is entirely dried, a porous scaffold with aligned elongated pores remains.
  • a porous scaffold remains with the desired elongated, aligned pore structure within the sample. At this point, the sample is still in its green body form and remains to be sintered. This is the final step of the freeze casting process, summarized in FIG. 3. Sintering is commonly a part of powder processing where a green body is heated to approximately 4/5 its melting temperature so that its particles fuse together.
  • Sintering greatly increases the mechanical properties of ceramic and metal freeze- cast samples. These properties are, in this case, influenced by the cell wall material properties and the cell wall and foam or honey-comb microstructure acquired after sintering. However, a full analysis on the various effects of processing parameters of sintering is beyond the scope of this thesis. Therefore, some effects will be summarized based upon the studies found in the literature conducted on the sintering of freeze-east materials. Typically, during sintering, the lamellae within the freeze-east scaffold, which are composed of a packing of fine particles and fine pores, will undergo densification and grain growth.
  • the extent of densification and grain growth is controlled by the rate of heating during sintering, the sintering time, and the final sintering temperature. As far as mechanical properties are concerned, densification of metals is correlated with an increase in strength and an increase in grain size is linked to a decrease in strength and an increase in ductility.
  • Sintering can be carried out in two different ways: with pressure and without pressure. Sintering under pressure is mainly done to achieve greater densification. However, freeze cast samples are sintered without applying any pressure to preserve the deliberate aligned porosity produced within the sample. Upon sintering it is expected that the particles fuse together so that densification occurs within the lamellae. On the other hand, it is anticipated that little change occurs regarding densification within the aligned, elongated pores. This is due to the fact that the pore widths are significantly larger than the size of the particles.
  • Binder removal can be achieved by heating the sample at a low temperature that is just high enough to burn off the binder. Another method is to use a low heating ramp rate to allow enough time for the binder to slowly burn off before the sintering temperature is reached. If the particles fuse together before the binder is sufficiently removed, pockets can form trapping the binder material within the sample.
  • FIG. 4 is an X-ray tomographic reconstructions of a freeze cast ceramic composite sample with a diameter of 0.6mm. Freezing rate: 20C/min (a) and 5C/min (b) in an embodiment.
  • FIG. 5 is a SEM image illustrating anisotropic growth of lamellar ice in an embodiment.
  • FIG. 6 is a simplified diagram illustrating lamellar crystals with their c-axis ( ⁇ 0001>) growing along a-axis ( ⁇ 1120>) in an embodiment.
  • Zone 1 is the region that is closest to the cold finger. It is a dense zone with no porosity. Located above this dense region is a transition into Zone 2, which is characterized by its closed cellular porosity. In Zone 3, another transition occurs where a lamellar microstructure is achieved.
  • Zone 2 the main area of interest, consists of elongated pores, aligned parallel to the freezing direction.
  • Polymer solution was prepared.
  • the polymer solution used to suspend the metal particles consisted of a combination of chitosan and gelatin dissolved in 1% acetic acid. It was found that chitosan offered a higher viscosity to suspend the particles in when compared to gelatin. However, it was shown that the addition of gelatin allowed for better mechanical properties in the sample's green body form after lyophilization. Furthermore, it was found that the combination of chitosan and gelatin in the 63/37wt% ratio resulted in the most homogenous final geometry after freeze drying of the various chitosan-gelatin ratios (50/50, 25/75, 75/25, 63/37 wt%) that were tested.
  • gelatin portion of the solution 5.5 g of gelatin powder were weighed out and transferred into a beaker with 100 ml of 1 vol% acetic acid to produce a 5.5% (w/v) gelatin solution.
  • a PTFE coated magnetic stir bar was inserted into the mixture and it was stirred on a hot plate stirrer at 60 rpm for 12 hours at a temperature of 35 C.
  • Slurries were prepared by mixing together constituents according to Table 1 A. Once all of the components of the slurry were measured and transferred into a mixing cup, the slurry was mixed and degassed in a high shear SpeedMixer (DAC 150 FVZ- K, FlackTek, Landrum, SC) at a speed of 2000 rpm for 60 seconds.
  • DAC 150 FVZ- K FlackTek, Landrum, SC
  • the sample was freeze dried.
  • the completely frozen sample was first removed from the copper cold finger by hand and then demolded using an arbor press with a wooden punch.
  • the sample was then transferred to a FreeZone 4.5 Liter Benchtop Freeze Dry System (Labconco, Kansas City, MO), where it was held at room temperature and at 0.180 mBar for at least 48 hours for the ice phase to sublime.
  • Sintering temperatures were at 1100°C, 1150°C, and 1175°C. It was determined that 1150°Cwas an adequate temperature for the sintering of the 316L stainless steel scaffolds. The process began at room temperature and then the
  • the samples were removed from vacuum and subjected to a reducing atmosphere of argon with 4% hydrogen (Ar about 4% 3 ⁇ 4).
  • samples were suitably sectioned into different shapes and sizes for mechanical and structural characterization. Samples were mechanically tested to determine the yield strength and Young's modulus of the sample. Additionally, the samples were structurally characterized to evaluate the
  • the sectioned cubes were tested in compression using an MTS 793 material testing system (MTS Systems Corp., Eden Prairie, MN) with a 5 kN load cell and a cross head speed of 0.025 mm/s, corresponding to a strain rate of 10" 3 /s.
  • MTS 793 material testing system MTS Systems Corp., Eden Prairie, MN
  • the samples were compressed in the direction parallel to the temperature gradient during freezing.
  • the compression platens were covered in PTFE tape prior to each compression test.
  • FIGs. 12A-C are three SEM images of 316L stainless steel scaffolds from the third sintering trial at 1150°C in an embodiment.
  • FIGs. 13A-B illustrate two SEM images of cross sections (perpendicular to the freezing direction) from samples S10 (a) and S10E (b) in an embodiment.
  • freeze-east samples of three different compositions S5, S10, and SIOE (all frozen at l°C/minute) were tested in compression. From the stress- strain curves, Young's modulus, yield strength, and plateau strength were determined. A typical stress-strain curve for a sample is shown in FIG. 16, indicating how the mechanical properties were determined.
  • Relative density is density of the porous material divided by the density of the solid from which it is made.
  • stainless steel foam has a 80% porosity which translates to a relative density of 0.8.
  • yield strength is plotted against Young's modulus. It is shown that by increasing the steel content from 5vol% (S5) to 10vol% (S10), higher mechanical properties can be achieved. However, this increase in solid loading was not necessary to achieve higher mechanical properties when analyzing samples S10 and S10E. With an identical amount of stainless steel loading and identical processing conditions, sample SIOE was almost twice as strong and over twice as stiff as sample S10. The reason for this may partially be because sample SIOE had a higher relative density, but further explanation was left to be determined by microstructural analysis.
  • FIG. 18 shows a plot of relative Young's modulus versus relative density. Once more, the different slopes in this graph correspond to the two different deformation behaviors in cellular materials. It can be seen that all of the samples fall significantly below the values predicted by theory.
  • SEM images of the samples revealed a large difference in pore structure between samples S10 and S10E. Pore sizes and cell wall thickness were measured, from SEM micrographs, as indicated in FIG. 14, revealing that with a thickness of 9 ⁇ 2 ⁇ the cell walls of S10 are about seven times thinner than those of SIOE, which are 60 ⁇ 9 ⁇ thick. Furthermore, it was found that S10 had an average lamellar spacing or short pore axis of 34 ⁇ 8 ⁇ , which is almost half of 69 ⁇ 8 ⁇ , the value for S10E.
  • FIGs. 15 a-d show four tomographic reconstructions of samples S10 (a, b) and SIOE (c, d). Images a and c show a full 3-D reconstruction of the samples. The colored planes on the cubes show a cross section perpendicular to the scaffold's freezing direction. Images b and d show these cross sections in 2D. The cubes and cross sections had 1 mm side lengths. FIGs. 15b and d show cross sections, perpendicular to the freezing direction, of samples S10 and S10E, respectively. It is shown that the lamellar spacings and wall thicknesses in sample S10 are significantly less than those of sample S10E.
  • sample S10 was created using a slurry similar to the one used in sample S5. To produce sample S10, an increased amount of stainless steel powder was used (10 vol%), double the volume used in sample S5 (5vol%). By increasing the solid loading in the slurry, an increase in relative density, from 0.168 to 0.215, was observed in the sintered samples S5 and S10, respectively.
  • Wall thicknesses in sample S 10 was measured to be, on average, 9 ⁇ , which is about seven times thinner when compared to the average wall thickness of 60 ⁇ as measured in sample S 10E. Furthermore, the average lamellae spacing, or short pore axis, in sample S 10E was observed to be 69 ⁇ , which was about twice the spacing observed in sample S10.
  • sample SIO and S10E Prior to sintering, they had equal relative densities, based on their equal volumes of solid loading. After sintering under identical conditions, sample SIO had a relative density of 0.215 and sample SIOE had an over 30% greater relative density of 0.281. This indicated that sample SIOE experienced greater densifi cation during sintering.
  • sample SIOE The greater densification in the case of SIOE is probably due to the larger amount of porosity in the cell walls prior to sintering, which was observed on SEM micrographs.
  • the thickness of the cell walls was limited to only about one to three particles, in contrast the cell walls of sample SIOE were closer to 20 particles thick and composed of randomly packed particles of varying size resulting in greater porosity within the cell walls.
  • sample SIOE experienced a greater shrinkage in cell wall dimensions, which also leads to a greater reduction in pore size when compared to sample S10, resulting in a greater relative density after sintering.
  • sample SIOE had a greater lamellae spacing and cell wall thickness. It was presumed that this was because the addition of ethanol into the polymer solution effectively lowered the freezing temperature of the slurry, therefore, altering the kinetics of the freezing process, the details of which are, at present, not entirely understood.
  • sample S10 had a much larger aspect ratio than sample S10E.
  • This variation in aspect ratios strongly contributed to the differences noted in mechanical properties, as detailed below.
  • Stainless steel freeze-east scaffolds as bone implant material It was mentioned in an earlier section that according to the literature, bone scaffold material should have at least 50% open porosity to promote tissue in growth, along with interconnected, aligned pores with a mean diameter of 100 - 400 ⁇ . Furthermore, since the scaffold will be used for a load bearing application, it must be able to support physiological loads. In this study, the samples produced showed great potential as a possible bone implant material. Samples S5, S10, and S 10E all fall in the desired property range and well inside the region of cancellous bone. Additionally, all three samples had an overall open porosity of at least 70% or more.
  • 316L stainless steel scaffolds were produced by freeze casting. With 70% porosity, these scaffolds achieved yield strengths of 32 MPa and Young's moduli of 940 MPa, values that fall into the strength and stiffness range of cancellous bone. The freeze casting process proved to be an ideal technique to produce custom-designed scaffold
  • Gelatin Solutions were prepared by dissolving 5.5% (w/v) gelatin in 1 % (v/v) glacial acetic acid (VWR International, West Chester, PA) in doubly distilled water. The gelatin solutions were mixed by magnetic stirring at 60 rpm for 12 hours at a temperature of 35°C prior to their use. Chitosan and gelatin solutions were mixed in a volume ratio of 4:1 in a high shear mixer (SpeedMixer, DAC 150 FVZ- , FlackTek, Landrum, SC) at a speed of 1600 rpm for 60 s to blend a 3 % (w/v) polymer solution consisting of 63wt% chitosan and 37wt% gelatin.
  • SpeedMixer SpeedMixer, DAC 150 FVZ- , FlackTek, Landrum, SC
  • America-Ceralox Division, Tuscon, AZ average diameter: 400 nm large spherical particles (Sigma Aldrich, St. Louis, MO) diameter: 5-10 ⁇
  • the particle sizes of the spherical alumina particles were chosen to represent the smaller (thickness) and larger dimensions (diameter) of the alumina platelets used in this study.
  • hydroxyapatite powder of spherical particles with an average particle diameter of 2.3 ⁇ was used (Trans-Tech, Inc., Adamstown, MD).
  • the suspensions were mixed and degassed in a shear mixer (SpeedMixer, DAC 150 FVZ-K, FlackTek, Landrum, SC) at a speed of 1600 rpm for 60s.
  • a shear mixer SpeedMixer, DAC 150 FVZ-K, FlackTek, Landrum, SC
  • Freeze casting ceramic-polymer slurries (12 mL) were pipetted into freezing molds directly before freeze casting.
  • the molds were placed on the cold finger of the freeze casting apparatus and allowed to adjust their temperature to 5°C which was the starting temperature of the cold finger.
  • the thermocouple and the band heater the temperature of the upper cold finger surface was decreased according to predefined cooling programs. Two different cooling rates were applied: l°C/min and 10°C/min. As the temperature of the cold finger was lowered below 0°C, ice nucleation started at the bottom plate of the mold and the slurries were directionally solidified from bottom to top. For both cooling rates, the temperature was decreased until a final freezing temperature of -80°C was reached. The molds were held at this temperature until the complete sample was solidified.
  • Freeze drying was performed after freeze casting.
  • the frozen samples were unmolded with a modified arbor press and transferred to a benchtop lyophilizer (FreeZone 4.5, Labconco, Kansas City, MO) where they were freeze-dried (lyophilized) for at least 48 hours.
  • the pressure within the system was 0.02 mBar and the cold trap was set to a temperature of -50°C.
  • the obtained scaffolds had a cylindrical shape with a diameter of 18 mm and a height of 35 mm. After lyophilization, the scaffolds had an average porosity of 91%.
  • Custom-made thermocouple mold equipped with 6 thermocouples along its height. The thermocouples were connected to a data acquisition unit where the temperatures measured at each thermocouple were recorded over time.
  • thermocouples were mounted along the height of a PTFE mold to monitor the
  • the particle self assembly in the honey-comb walls was determined and the pore structure and mechanical properties measured after processing with cooling rates of 1 °C/min and 10°C/min which correspond to freezing front velocities of 7.4 ⁇ /s and 27.7 ⁇ /s, * respectively.
  • FIGs. 9A-C are SEM micrographs of composite cell walls of hybrid scaffolds made from a) small particles b) bimodal particles c) large particles. Scale bar is 5 ⁇ . The SEM micrographs of the three different scaffold types reveal significant differences in the wall architecture.
  • the size of the small particles is much smaller than the wall thickness and the particles are thus incorporated into the wall structure, glued together by the polymeric matrix (see Table 2). Between 5 and 15 layers of particles make up the walls with a thickness of 2 to 7 micrometers.
  • the cell walls consist only one layer of particles. They are incased and interconnected by a polymer membrane.
  • the walls made from the bimodal composition are a combination of the two.
  • the polymer membrane between the large particles includes several layers of small particles and the wall thickness is smaller in comparison to the small particle scaffolds because of the smaller amount of small particles that have to be accommodated within the walls.
  • Table 2 Wall thickness in dependence of the particle size and freezing rate as determined with scanning electron microscopy.
  • FIG. 10 and FIG. 11 show Young's modulus for scaffolds including different particles sizes and size distributions, frozen at two different freezing rates of l°C/min and 10°C/min.
  • FIG. 22 Scaffold structure is shown in FIG. 22:
  • the created freeze-east scaffolds indeed possessed a lamellar structure with composite walls of highly aligned alumina platelets glued together by the polymeric phase.
  • the lamellar spacing was the same as previously determined for the scaffolds including spherical particles with 28 ⁇ for a freezing rate of 10°C/min and 34 ⁇ for a freezing rate of l°C/min.
  • the nacre-like arrangement of the platelets in the walls is evident, however, due to cutting damage, several lamella show rugged edges with platelets or small pieces of the lamellae that were pushed over the interlamellar spaces.
  • a focused ion beam (FIB) system was used to cut a window into a single lamella.
  • the beam current of the FIB (Strata DB235, FEI Company, Hillsboro, OR, USA) was set to 50 pA and an accelerating voltage of 30kV was used.
  • FIG. 23C shows a close-up of the cross-section, revealing the arrangement of platelets and the thickness of the lamella.
  • the platelet-composite walls indeed possess the desired nacre-like arrangement of highly aligned platelets glued together by the polymeric phase. As estimated from the SEM images the wall has a thickness of approximately ten platelets.
  • FIG. 16 shows typical stress/strain curve of the investigated hybrid scaffolds. Young's modulus was determined from the initial linear region of the curve while the yield strength was taken as the stress at which the material left the linear region and the slope of the curve changed significantly. Toughness was determined as the area under the stress-strain curve up to a strain of 60%.
  • FIG. 20 shows Young's modulus and yield strength for the porous hybrid materials including small, bimodal and large particles as well as platelets.
  • the platelets achieve the highest stiffness and strength while the small particles possess the lowest values.
  • FIG. 20 illustrates results from compression tests on porous composites.
  • the mechanical properties can be significantly varied through different particle size distributions and freezing rates. Both modulus and strength increase with an increase in the freezing rate for the composites with small (CAS) and bimodal (CAB) particle sizes, but stay constant for large particles (CAL). For both freezing rates, the small powders or particles resulted in the material with the lowest mechanical properties (CAS). At 1 °C/min, the composite with the large particles (CAL) achieved both the highest modulus and the highest strength with 14 MPa and 0.23 MPa, respectively. At 10°C/min, the scaffolds with the bimodal particle distribution (CAB) had with 20 MPa and 0.27 MPa the highest respective values. These property differences are due to differences in particle sedimentation speed, freezing front velocity, and, very importantly, the arrangement of particles in the lamellae.
  • FIG. 8 is a plot of plateau strength against Young's modulus for scaffolds including different particles sizes of particles and size distributions, frozen at two different freezing rates of l°C/min and 10°C/min in an embodiment.
  • Freeze casting capitalizes on directional solidification.
  • a solution or slurry is frozen, pure ice crystals form, rejecting dissolved or dispersed matter into intercrystalline spaces.
  • Subsequent freeze-drying removes the ice but preserves the lamellar or tubular porosity that it templated.
  • Directional solidification of the ice results in a honey-comblike structure with anisotropic mechanical properties.
  • Material composition, additives and freezing rate allow to tune overall porosity, pore size and pore geometry.
  • Water-based biopolymer solutions of chitosan and gelatin where used as both binders and polymer matrix. Ceramic particles of three different particle size
  • Hybrid scffolds were prepared using two different cooling rates:
  • Freeze casting of platelet-based slurries creates highly porous scaffolds with a nacre-like cell wall structure due to self-assembly during processing.
  • the "cellular nacre” possesses properties considerably higher than those of composite scaffolds of the same composition made with spherical particles. They offer tremendous potential for use in applications, which require a combination of high porosity, stiffness, strength and toughness, such as filters, catalyst carriers and tissue scaffolds.
  • the freeze-east material benefits from a complex, hierarchical architecture that, up to now, has been difficult to emulate in bulk materials.
  • the freeze casting of platelet slurries produces highly porous cellular materials with self-assembled nacre-like cell walls and property profiles.
  • the self- assembly happens during the ice-templating of the platelets that are of the same dimensions as the mineral building blocks in natural nacre (FIG. 23B).
  • the directional solidification during freeze casting causes a phase separation to occur in the platelet- slurry.
  • Lamellae of pure water-ice grow, alternating with lamellae of a ceramic-polymer composite, causing the platelets to self-assemble into a nacre-like structure.
  • the ice phase is removed through sublimation with a freeze dryer, leaving behind a porous ceramic-polymer composite scaffold.
  • alumina powder consisting of either spherical particles or platelets were added to the chitosan-gelatin solution to achieve a dry weight ratio of 9:0.64:0.36 (alumina: chitosamgelatin), or 9:1 (alumina:biopolymer).
  • the alumina platelets had a diameter and a thickness of 5-10 ⁇ and 300-500 nm respectively (AlusionTM, Antaria Limited, Bentley, Western Australia).
  • the spherical particle scaffolds were made either from small particles with a diameter of 400 nm (Ceralox SPA-RTP SB, Sasol North America Inc., Arlington, AZ, USA), large particles with a diameter of 10 ⁇ (Sigma Aldrich, St. Louis, MO, USA), or a bimodal distribution with a 7:3 large:small particle volume ratio.
  • the two particle sizes were chosen to match the thickness and the diameter of the platelets used in our study, which have dimensions that closely resemble those of the aragonite platelets in Abalone nacre.
  • the two freezing rates of l°C/min and 10°C/min resulted in a lamellar spacing of 34 ⁇ and 28 ⁇ , respectively (FIG. 25).
  • the overall sample porosity ranged from 90.2-91.8% and the composition of the cell wall solid was 75% alumina and 25% polymer by volume.
  • both CAS and CAL samples had about the same volumetric composition:, i.e. 90% porosity, 7.6% A1 2 0 3 , and 1.5% chitosan, 0.9% gelatin
  • both CAS and CAP samples had about the same outer diameter of 18.44 mm. They were sintered at identical conditions, actually, in the very same same sintering cycle. After sintering, the CAS sample has an outer diameter of 14.39 mm while the CAP sample has an outer diameter of 17.51 mm.
  • the volumetric shrinkage for the CAS sample is 39% while the CAP sample had a volumetric shrinkage of only 10%.
  • the linear shrinkage is 22% for small particles while for the platelets the linear shrinkage is 5%.
  • FIG. 38 illustrates CAS and CAP samples.
  • FIG. 39 shows a sintering cycle for CAS and CAP in an embodiment.
  • Alumina platelets in chitosan-gelatin slurries were prepared as described above. Several drops of the slurry were pipetted onto a microscope slide, which was covered by a second slide to form a Hele-Shaw cell. The slides were compressed from both sides to achieve a uniform sample film thickness of about 100 ⁇ . The Hele-Shaw cell was mounted horizontally in a custom-designed holder to expose the included slurry to a liquid nitrogen bath at one end of the microscope slides.
  • x 1 mm x 5 mm were cut with a diamond wire saw so that the 5 mm dimension was oriented parallel to the freezing direction.
  • the sample was mounted upright on a cylindrical metal holder and placed in a SkyScan 1172 high-resolution desktop micro- computed tomography system (SkyScan, Kontich, Belgium). Radiographs were taken at a voltage of 59 kV, a current of 167 ⁇ and a pixel size of 1.47 ⁇ . An exposure time of 2356 ms and a frame averaging of 5 was used. The rotational step size was 0.15°.
  • the SkyScan software NRecon was used for tomographic reconstruction. Volume renderings were prepared and visualized with the Avizo® Standard software package (VSG, Visualization Science Group, Inc., Burlington, MA, USA). Table 3
  • a 9% volumetric expansion occurs when the water solidifies into ice. Because the lateral expansion of the material is constrained by the mold, the volume increase of the solid phase must result in a flow of the, at this point, still liquid or viscous composite slurry. This flow causes the platelets to align and self-assemble.
  • FIG. 23A illustrates schematic of platelet self-assembly between ice crystals during directional solidification.
  • FIG. 23B illustrates ice crystals (black) grow through the slurry along the direction of the temperature gradient. The lateral growth of the ice crystals concentrates the interlamellar ceramic-polymer composite (white). Scale bars are 100 ⁇ .
  • FIG. 23C illustrates scanning electron micrograph of an individual composite lamella. The cross-section of the nacre-like microstructure was created with a focused ion beam (FIB) system. It reveals the high degree of alignment of the platelets. Scale bar is 5 ⁇ .
  • FIG. 23C illustrates mechanical performance of the nacre-like composite scaffolds. Platelet scaffolds (P) are compared with scaffolds of the same composition made from small (S), bimodal (B) or large (L) spherical particles. Freezing rates were l°C/min (black) and 10°C/min (red).
  • the cell walls had the desired brick-and-mortar structure of highly aligned platelets in a polymer matrix (FIGs. 23 A and 23C).
  • the Young's modulus, yield-strength and toughness of the platelet scaffolds were found to be higher by a factor of two to four (FIG. 23 D). Therefore, freeze casting of platelets provides significantly improved mechanical properties than freeze casting spherical particles.
  • FIG. 24 is a typical stress-strain curve of a freeze-east scaffold tested in compression, indicating how Young's modulus, yield strength and toughness were determined.
  • FIG. 25 shows volume rendering of the cellular structure of a typical freeze-east platelet scaffold. X-ray microtomography data visualized with the Avizo® Standard software package. Edge length of the cube is 500 ⁇ .
  • Results showed ultra-low thermal conductivity values between 0.05-1 W/(m*k), excellent reflectivity (>85%) in the visible NIR range, and sufficient mechanical strength to sustain its own weight.
  • Optical and SEM imagery clearly show the regular spacing of the pores and the alignment of the lamellae.
  • X-ray tomography also confirms this.
  • the process is scalable, and the base component materials are inexpensive and relatively green. Applications include specialty needs for materials with low densities, low thermal conductivity, optically reflection and acoustically dampening.
  • HGMS Hollow glass microspheres
  • Freeze casting is one method by which porous composite materials are made. It consists of the directional freezing of an aqueous slurry containing composite components such as polymers, ceramic or metallic particles.
  • the benefits of using an ice-template for the creation of a porous material is that it results in highly aligned porosity in the growing direction of the ice crystals. This alignment of the particles comes about by the lamellar structure formed by the ice which leads to a form of self- assembly. The self-assembly also brings about enhanced mechanical strength in the growth direction through a honey-comb like structure. Freeze-east products may need to be lyophilized in order to achieve their porosity.
  • Lyophilization is the process of freeze drying, which uses a vacuum pump to put the material under low pressure and remove the water via sublimation.
  • Sublimation is the transition of a substance directly from its solid state to its gaseous phase, without going through the liquid phase. This direct transition from ice to gas reduces damage to the structure due to the formation of the liquid phase.
  • the end result of the freeze-casting process is a highly aligned porous composite material, comprised of the non-aqueous components, packed together in a honey-comblike structure dependent on the starting water content and the freezing rate. These porous materials have been known to achieve porosities >90%, ultra light-weights compare to their solid counter parts and properties highly dependent on the material components within.
  • Glass spheres may increase reflectance of visible and IR light. This occurs by light scattering in materials, which is primarily a function of three mechanisms, specular reflection, diffuse reflection, and total internal reflection. Specular reflection, or reflection off a mirror-like surface in a single direction, applies poorly to freeze-east porous composite structures made of silicon micro bubbles and bio-polymer. Diffuse reflection is the scattering of light in many directions due to striking an uneven surface. Total internal reflection is an optical phenomenon that occurs when light is attempting to pass from a medium of higher index of refraction to one of lower index and is encouraged by the spherical geometry of the spheres.
  • the freeze-east porous samples may have diffuse reflectance and total internal reflection. Internal reflection may occur between the interface of the glass spheres and air. While porous structure itself, embedded with glass spheres will provide a roughened surface upon which diffuse reflectance occurs. This reflection of light in general may affect heat transfer through the material, possibly lowering the conductivity even more.
  • HGMS 2 ⁇ m-diameter solid glass sphere
  • SGMS 2 ⁇ m-diameter solid glass sphere
  • 5 ⁇ - diameter glass thin flake Some properties of these particles can be found in Table5 .
  • Four subdivisions or sample groups were designated from these particles. The four groups were: first a HGMS group, herein known as group 1, second 2.5 ⁇ SGMS group, group 2, a thin flake group, group 3, and a bimodal group of both HGMS and 2.5 ⁇ SGMS, group 4.
  • HGMS 2 ⁇ m-diameter solid glass sphere
  • a 5 ⁇ - diameter glass thin flake Some properties of these particles can be found in Table5 .
  • Four subdivisions or sample groups were designated from these particles. The four groups were: first a HGMS group, herein known as group 1, second 2.5 ⁇ SGMS group, group 2, a thin flake group, group 3, and a bimodal group of both HGMS and 2.5 ⁇ SGMS, group 4.
  • For bimodal packing particles with a ratio
  • Chitosan polymer is being used as the polymer phase. Chitosan is a green, renewable bio-polymer produced from the shells of crustaceans. It also happens to be the 2 nd most abundant polysaccharide on the planet derived from Chitin found in crustaceans. Low molecular weight chitosan, 75-85% deacetylated, (Sigma Aldrich, St. Louis, MO) was used as received. A magnetic stirrer at 60 rpm for 24 hours was used to mix the chitosan solutions. After initial stirring of the solutions, they underwent shear mixing at a speed of 1600 rpm for 60 s in a DAC 150 FVZ-K SpeedMixer (FlackTek, Landrum, SC).
  • the glass particles were functionalized using a 3
  • APTES Aminopropyltriethoxysilane(APTES)/acetone solution with a 1 :10 ratio per milliliter of amine. 2.9 grams of glass particles were weighed using a Mettler Toledo Excellence Plus XP Analytical Balance and added to a 22ml solution of APTES/acetone. The silane was acquired from Sigma Aldrich. The solution was then allowed to functionalize at room temperature for 2 hours, with slight agitation approximately every 30 minutes. To remove the HGMS and flake particles from solution, a Pyrex 4-5.5 ⁇ ceramic filter was used in conjunction with a vacuum assisted round-bottom flask, to separate the un-functionalized APTES/acetone solution.
  • the particles were then washed a minimum of 3 times to remove any remaining un-functionalized APTES.
  • a centrifuge was used to separate the particles from solution, which was then decanted. After being decanted, an additional 30 mi's of acetone was added and the solution agitated to wash the particles. The solution was centrifuged again and
  • the samples are characterized via mechanical, physical, thermal, and optical techniques. Mechanical testing is performed on Instron 4222 (Instron, Norwood, MA) using a 0.05mm/sec cross-head speed and a 50 N load cell. Samples are prepared as a 5mmx5mmx5mm cubes and tested compressively along the growing direction of the sample. Samples are tested dry and at room temperature (25 C), although the option of wet testing is possible for future work. The Young's modulus and yield strength are determined from the resultant data. Two layers of four cubes per layer were cut and tested from each sample.
  • 3mmx3mmx2mm dimensions were prepared for SEM imaging. Each sample was grounded with silver paint, and coated with a layer of platinum and graphite before being examined in the SEM. X-ray Microtomography was first performed on
  • 5mmx5mmx5mm cubes and later changed to 2mmx2mmx2mm cubes for higher resolution imaging.
  • Optical images were taken from the same 5mmx5mmx5mm cubes as used in the Instron.
  • specific heat measurements are measured using a Quantum Design heat capacity measuring system, while thermal conductivity is measured by a Quantum Design P670 Thermal Transport System.
  • the specific heat samples were prepared as 3x3x2mm blocks.
  • Thermal conductivity samples were prepared as 6rnmx6mmx 1 mm sheets. Two layers of thermal conductivity samples and specific heat samples were cut from each sample. One layer was taken from near the top of the sample, the other from near the bottom. Measurements were made at room temperature under high vacuum ( ⁇ 1 e ⁇ torr).
  • a Perkin Elmer Lambda 950 UV-Vis-NIR Spectrophotometer with a 60mm integrating sphere attachment was used to determine and compare the reflectance of radiation in the 250 nm-2500 nm range of interest. Both deuterium and tungsten lamps were used to scan this wide range. This range incorporates the entirety of the visible light spectrum, as well as some wavelengths in the ultra-violet and near-infrared. A gain of 4 was used on the NIR detector with a response time of 0.2 s.
  • Optical properties were measured.
  • the scan measured percent reflectance (%R) of the material, spanning from 250 nm to 2500 nm, a broad spectra of UV-Vis-NIR wavelengths.
  • the samples were mounted on the blank side of a white 3x5 card with double sided scotch tape and covered by another 3x5 card with a cut out hole to the approximate size of the sample. This was done in an effort to minimize reflectance measurements off the double-sided tape, and to ensure that diffuse reflections were only coming off the white card and the sample. This simple rig was inserted into the opening of the diffuse reflectance sphere and held in place by spring-loaded arm.
  • Spectralon backing a highly reflective fluoropolymer which according to its profile on the manufacturer's website (Labsphere) is >95% reflective in the 250 nm to 2500 nm range. Spectralon was also used as the reference material for every test. The results are shown in FIG. 26.
  • FIG. 27A-27B is a plot of Log Avg. Yield Strength vs. Log Avg. Modulus for the samples.
  • the thermal conductivities were measured to be extremely low, between .05 and .1 W* m" ' ⁇ "1 , as nearly as low as Aerogels.
  • the reflectivity of the samples was characterized to be in the range of 80-89% in the visible and near IR range.
  • the composite has also been shown to be mechanically and structurally stable able to support its own weight. Through freeze-casting, a highly aligned porous microstructure in a composite was also obtained. Optical and electron microscopy have both shown evidence of successfully aligned porosity and regular pore spacing, while X-ray tomography has shown the depth of the interpenetrating pores throughout the specimen.
  • Possible applications include, but not limited to, high-end thermal and radiation shielding, as well as thermally insulated applications. This material may find uses in high-end specialty applications that require low densities, low thermal
  • Tissue scaffolds, filters, and insulating materials required a high degree of porosity.
  • porosity in a material significantly decreases the mechanical performance.
  • Capitalizing on a directional, honey-comb-like structure allows for the maximization of mechanical properties while maintaining open porosity.
  • the choice of materials and the use of freeze casting help achieve highly porous materials with independently tunable mechanical (stiffness, strength, toughness), structural (overall porosity, pore size), and chemical performance for a wide range of applications.
  • Nanocellulose fibers are derived from the load bearing cellulose fibers in plant cell walls, have diameters ranging from 4 to 40 nm.
  • Chitosan is deacetylated chitin, which is the structural polysaccharide that provides the exoskeleton of insects and crustaceans with stiffness and strength.
  • Freeze casting creates aligned open porosity in the direction parallel to the freezing direction (See FIG. 30). The structure is controlled through the freezing rate as well as through the constituent materials. Nanocellulose (NC), Chitosan (CS), Chitosan (CS) + Nanocellulose (NC), and Nanoclay (MTM) + Nanocellulose (NC) materials were used to investigate this structural difference, as well as the influence on mechanical performance.
  • Anisotropic mechanical properties include strength, modulus, and toughness. Freeze cast scaffolds, in their strong direction, outperform isotropic foams at the same composition and porosity with respect to their Young's modulus (stiffness), strength, and toughness (i.e. work to fracture) (See FIG. 31).
  • Nanocellulose improves both Young's modulus and yield strength in chitosan (CS) and nanoclay(MTM) based materials (See FIG. 32, where dashline are for a traverse direction and solid lines are for longitudinal direction) .
  • Nanocelluose can further increase the toughness and structural stability of hydroxyapatite (HAp) materials for applications as bone tissue scaffolds.
  • HAp hydroxyapatite
  • Nanocellulose reinforced chitosan and hydroxyapatite scaffolds showed the highest toughness (inset).
  • Freeze casting, or ice-templating allows for the creation of directional structure, interconnected porosity, with maximized mechanical properties. Reinforcement with nanocellulose yields enhanced mechanical properties, especially toughness.
  • Advanced burner reactors are designed to reduce the amount of long- lived radioactive isotopes that need to be disposed of as waste.
  • the input feedstock for creating advanced fuel forms comes from either recycle of used light water reactor fuel or recycle of fuel from a fast burner reactor.
  • Fuel for burner reactors requires novel fuel types based on new materials and designs that can achieve higher performance requirements (higher burn up, higher power, and greater margins to fuel melting) than currently achieved.
  • One promising strategy to improved fuel performance is the manufacture of metal or ceramic scaffolds that are designed to allow for a well defined placement of the fuel into a host, which permits greater control than that possible in the production of typical CERMET fuels.
  • a nuclear fuel may be placed into the metal honeycomb structures as the basis of a CERMET fuel or a purely metallic fuel.
  • ceramic honey-comb structures are formed as the basis of an inert matrix fuel (IMF) form or a form for containing isotopes targeted for geologic disposal.
  • IMF inert matrix fuel
  • the metal honey-comb structures and the ceramic honey-comb structures are formed by the freeze-casting, or ice-templating, which enables establishing a range of flexible and controllable fuel pellet designs.

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Abstract

L'invention porte sur un échafaudage composite de métal-polymère qui comprend des particules métalliques couplées avec un liant polymère, l'échafaudage présentant des régions de porosité alignée avec un gradient. Dans un mode de réalisation particulier, les particules métalliques comprennent de l'acier inoxydable. Les particules métalliques présentent des tailles inférieures ou égales à 3 μm. L'échafaudage possède un module de Young inférieur à 950 MPa. Le liant polymère comprend du chitosane et de la gélatine. Le composite comprend également de l'éthanol. Le composite possède une porosité d'au moins 70 %. L'invention porte également sur des systèmes et sur des procédés de production d'un tel échafaudage composite de métal-polymère.
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